This invention relates to vehicle brake systems, and more particularly to vacuum boosters for vehicle brake systems.
Vehicles such as automobiles, trucks, buses, and motor homes typically include a dashboard at the front of the passenger compartment, having a power brake booster on the front of the dashboard connected by a push rod to a brake pedal mounted on the rear of the dashboard in the passenger compartment. A brake master cylinder, connected to the braking system, is mounted on the front end of the booster.
As shown in FIG. 1, one commonly used type of brake booster 10, known as a vacuum booster, includes a housing apparatus 12 having a front housing 14 and a rear housing 16, joined together and defining a longitudinal axis 18 of the booster 10. The front housing 14 defines a front wall 20 of the housing 12 and an inner surface 22 of the front wall 20. The rear housing 16 defines a rear wall 24 of the housing 12 and an inner surface 26 of the rear wall 24.
A tie rod 28 extends axially through holes 25, 27 in the front and rear walls 20, 24 respectively of the housing 12. The tie rod 28 has a first end 30 engaging the rear wall 24 of the housing 12, and a second end 32 engaging the front wall 20 of the housing 12. The first end 30 of the tie rod 28 includes an annular flange 36 welded or mechanically fastened to the inner surface 26 of the rear wall 24, and a threaded section 34 extending from the annular flange 36, through the hole 27 in the rear wall 24, for mounting the booster 10 on the front of a vehicle dashboard. The second end 32 of the tie rod 28 extends through the hole 25 in the front wall 20 of the housing 12, and is also threaded to receive a special sealing nut 38 that bears against the inner surface 22 of the front wall 20. The threaded portion of the second end 32 of the tie rod 28 extends outward beyond the front wall 20 of the booster 10, for mounting a brake master cylinder to be actuated by the booster 10.
During assembly of the booster 10, the position of the sealing nut 38 on the threads at the second end of the tie rod 28 is adjusted so that once the front and rear housings 14, 16 are joined together, the sealing nut 38 will be properly positioned for applying an axially directed force against the inner surface 22 of the front wall 20 of the housing 12 to achieve a desired axial distance between the front and rear walls 20, 24 of the housing 12. Setting the front and rear walls 20, 24 at a desired axial distance is required to allow proper pre-load of the front and rear housings 14, 16, and proper spacing between internal components of the booster 10, such as the booster piston 40 and a first and second diaphragm support 42, 44 that move with the piston 40, so that the booster 10 can function properly.
The booster 10, of FIG. 1, is a tandem vacuum brake booster having a primary and a secondary diaphragm 46, 48, and a divider 41 that separate the interior of the housing 12 into primary and secondary vacuum chambers 50, 52, and primary and secondary high-pressure chambers 51, 53. These chambers must be sealed from one another for proper operation of the booster 10. Air tubes 54, adapted for sealing engagement with the primary diaphragm 46 and the divider 41 of the booster 10, provide sealed passageways for the tie rod 28 to pass through the primary vacuum and high pressure chambers 50, 51, without allowing leakage along the tie rod 28 between the primary vacuum and high pressure chambers 50, 51. A sliding seal 55, between the secondary diaphragm 48 and the tie rod 28, precludes leakage around the tie rod 28 between the secondary vacuum and high pressure chambers 52, 53. Maintaining the proper positioning of internal components, such as the air tubes 54, while adjusting the position of the sealing nut 38 on the tie rod 28, further complicates the process of setting the proper distance between the front and rear walls 20, 22 of the booster 10.
What is needed, therefore, is an improved method and apparatus for setting and maintaining the axial distance between the front and rear walls of a booster housing in a vacuum booster of the type described above.
Our invention provides a tie rod apparatus and method for adjusting the axial distance between the front and rear walls of the booster, from outside of the booster, after the booster has been assembled.
In one form of our invention, a vacuum booster includes a housing having a front housing and a rear housing joined together and defining a longitudinal axis of the booster. The front housing defines a front wall of the housing and an inner surface of the front wall. The rear housing defines a rear wall of the housing and includes a captive nut having threads adapted for threaded engagement with a threaded end of a tie rod. The front and rear walls are spaced an axial distance from one another along the longitudinal axis. A tie rod extends axially through the housing and has a first end engaging the rear wall of the housing and a second end engaging the front wall of the housing. The first end of the tie rod has threads for engaging the threads of the captive nut in the rear wall of the housing. The second end of the tie rod has an axially facing surface thereof for applying an axially directed force against the inner surface front wall of the housing. The axial distance of the housing between the front and rear walls of the housing is adjusted by turning the tie rod, to thread the first end of the tie rod farther in or out of the captive nut.
In another form of our invention the booster includes internal elements thereof axially separating the interior of the housing into fluid chambers sealed from one another, and the captive nut includes a tube extending axially therefrom along a part of the tie rod into the interior of the housing through one or more of the fluid chambers. The tube has a surface adapted for sealing engagement with the internal elements of the booster.
The foregoing and other features and advantages of our invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawing. The detailed description and drawing are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.